With the new system, all stock changes due to orders from any source are notified to all channels.  Stock changes due to stock received are only notified to channels if below the threshold.

e.g.

Assuming the notification threshold is 20:

You have 5 of an item in stock and its listed on Ebay and Amazon as 5 in stock.

You receive an order for 1 of the item reducing the stock availability to 4.  We notify Ebay and Amazon stock is now 4.

You receive a delivery of 16 taking total stock to 20.  We notify Ebay and Amazon stock is now 20.

You receive a delivery of 2 taking total stock to 22.  We no longer notify Ebay and Amazon about this – they already know about the 20.

You receive an Amazon order so Amazon reduce their stock figure to 21.  COMS stock reduced to 21.  We notify Ebay and Amazon stock is 20.

You receive an Ebay order so Ebay reduce their stock figure to 19. COMS stock reduced to 20.  We notify Ebay and Amazon stock is now 20.

You receive an Amazon order so Amazon reduce their stock figure to 19. COMS stock reduced to 19. We notify Ebay and Amazon stock is now 19.

You find a broken item in the warehouse so manually correct the COMS stock to 18.  We notify Ebay and Amazon stock is now 18.

For a while after we launched this new stock management process, the threshold was set to 10 items.  

If an item received a stock update which the threshold was 10, we will have told Amazon stock is 10, but as the threshold is now 20, unless the item has received a stock update since we changed the threshold we won't have notified Amazon - so it will still show 10 at Amazon.  Next time the stock is updated for this item (either manually or from an order) we will update Amazon to be either the real stock or 20.